Veins can be broadly divided into three categories: the deep veins, which are the primary conduit for blood return to the heart; the superficial veins, which parallel the deep veins and function as a channel for blood passing from superficial structures to the deep system; and topical or cutaneous veins, which carry blood from the end organs (e.g., skin) to the superficial system. Veins are thin-walled and contain one-way valves that control blood flow. Normally, the valves open to allow blood to flow into the deep veins and close to prevent back-flow into the superficial veins. When the valves are malfunctioning or only partially functioning, however, they no longer prevent the back-flow of blood into the superficial veins. This condition is called reflux. As a result of reflux, venous pressure builds within the superficial system. This pressure is transmitted to topical veins, which, because the veins are thin walled and not able to withstand the increased pressure, become dilated, tortuous or engorged.
In particular, venous reflux in the lower extremities is one of the most common medical conditions of the adult population. It is estimated that venous reflux disease affects approximately 25% of adult females and 10% of males. Symptoms of reflux include varicose veins and other cosmetic deformities, as well as aching, itching, and swelling of the legs. If left untreated, venous reflux may cause severe medical complications such as bleeding, phlebitis, ulcerations, thrombi and lipodermatosclerosis.
Endovascular thermal therapy is a relatively new treatment technique for venous reflux diseases. With this technique, thermal energy generated by laser, radio or microwave frequencies is delivered to the inner vein wall causing vessel ablation or occlusion. Typically a catheter, fiber or other delivery system is percutaneously inserted into the lumen of the diseased vein. Thermal energy is delivered from the distal end of the delivery system as the device is slowly withdrawn through the vein. Although the device description described herein focuses on endovenous treatment using laser energy, other thermal energy forms may be used.
The procedure begins with an introducer sheath being placed into the main superficial vein, called the great saphenous vein, at a distal location and advanced to within a few centimeters of the point at which the great saphenous vein enters the deep vein system, (the sapheno-femoral junction). Typically, a physician will measure the distance from the insertion or access site to the sapheno-femoral junction on the surface of the patient's skin. This measurement is then transferred to the sheath using tape, a marker or some other visual indicator to identify the insertion distance on the sheath shaft. Other superficial veins may be accessed depending on the origin of reflux.
The sheath is placed using either ultrasonic guidance or fluoroscopic imaging. The physician inserts the sheath into the vein using the visual mark on the sheath as an approximate insertion distance indicator. Ultrasonic or fluoroscopic imaging is then used to guide final placement of the tip relative to the junction. Positioning of the sheath tip relative to the sapheno-femoral junction or other reflux point is critical to the procedure because the sheath tip position is used to confirm correct positioning of the fiber when it is inserted and advanced. Current art sheath tips are often difficult to clearly visualize under either ultrasonic guidance or fluoroscopic imaging.
Once the sheath is properly positioned, a flexible optical fiber is inserted into the lumen of the sheath and advanced until the fiber tip is near the sheath tip but still protected within the sheath lumen. The fiber includes a red aiming beam at the tip that is used to visualize the location of the fiber tip within the vessel lumen as it is advanced to the sapheno-femoral junction through the properly positioned sheath lumen. When activated, the aiming beam appears as a red glowing light visible through the skin surface. One problem with the use of a conventional sheath is that the sheath material often blocks the red aiming beam from being clearly visible on the skin surface as the fiber is advanced through the sheath.
Prior to the application of thermal energy, tumescent anesthesia is injected along the entire length of the vein into space between the vein and the surrounding perivenous tissue. A mixture of saline and 0.1-0.5% lidocaine or other similar anesthetic agent is typically used. Tumescent anesthesia serves several functions. The fluid anatomically isolates the vein, creating a barrier to protect the tissue and nerves from the thermal energy. Specifically, the fluid provides a heat sink to prevent thermal injury to adjacent non-target tissues, nerves and the skin surface. Extrinsic pressure from the fluid also compresses the vessel, reducing the vein diameter, minimizing the volume of the vein, and maximizing the heat affect to the vein walls. Finally, the lidocaine mixture, with its anesthetic characteristics, reduces patient pain during the procedure.
The tumescent injections are typically administered every few centimeters along the entire length of the vein under ultrasonic guidance. Ultrasound is used to visualize the vein, confirm proper location of the needle tip in the perivenous space, and to determine correct injection volumes. After the user has confirmed that the needle tip is correctly positioned between the vein and perivenous tissue through ultrasonic imaging, the tumescent fluid is slowly injected. Again, visualization of the target perivenous space is often difficult, and the user may inadvertently puncture the sheath wall with the needle tip during placement. The delicate fiber may also be damaged by incorrect placement of the needle.
Once the combined sheath/optical fiber assembly is properly positioned and after the administration of tumescent anesthesia as described above, thermal energy can be applied to the vein. To treat the vein, a laser generator is activated causing energy to be emitted from the distal end of the optical fiber into the vessel. The energy reacts with the blood remaining in the vessel and causes heat, which damages the vein wall which, in turn, causes cell necrosis and eventual vein collapse. With the energy source turned on, the sheath and fiber are slowly withdrawn as a single unit until the entire diseased segment of the vessel has been treated.
Currently available sheaths for endovascular laser treatment of reflux have several drawbacks. One problem is the difficulty in visualizing the sheath and particularly the tip as it is positioned just proximal to the sapheno-femoral junction. Although some currently available sheaths may be visible under fluoroscopic guidance, these same sheaths are not optimized for use with ultrasonic imaging modalities. The visibility of the tip under either fluoro or ultrasound is very important when placing the tip relative to the sapheno-femoral junction. Incorrect placement may result in either incomplete occlusion of the vein or non-targeted thermal energy delivery to the femoral vein, which may result in deep vein thrombosis and its associated complications including pulmonary embolism. Another possible complication of a misplaced device is possible vessel perforation.
Another problem with conventional sheaths is that they have shaft colorant. The colorant results in difficulty visualizing the red aiming beam on the skin surface due to partial or complete blocking of the beam by the colored material.
Sheaths that are sold with endovascular laser treatment kits do not contain any shaft reinforcement to increase torquability, durability and kink resistance during insertion and placement within the vein. A reinforced sheath shaft is also desirable to provide a durable, protective barrier to the delicate fiber during tumescent injections, which are administered along the length of the vessel being treated.
Most prior art sheaths do not include any measurement indicator for the physician to determine the approximate length the sheath should be inserted into the vein to be positioned just proximally of the sapheno-femoral junction. Without any measurement indicator, the physician must manually mark the sheath's surface using adhesive tape or other means to indicate maximum insertion length. In addition, most prior art sheaths do not provide a simple, easy mechanism for determining the rate at which the sheath/optical fiber assembly should be withdrawn through the vein during the actual treatment step.
Therefore, it is desirable to provide an endovascular treatment sheath and method that provides for optimized visibility under fluoroscopic imaging or ultrasound imaging or preferably under both. The sheath should be designed to provide easy visual identification of the sheath location for precise positioning relative to the sapheno-femoral junction or other vessel target. Specifically, the sheath tip should be easily visible under either ultrasound or fluoroscopic imaging. The sheath should not block or decrease visibility of the aiming beam during fiber insertion through the sheath. The sheath should also be durable and resistant to needle punctures. The sheath should also be constructed to optimize torquability and kink-resistance during insertion and withdrawal. The device should also provide an easy, simple way for the physician to approximate insertion length and assess pullback rate during the procedure. In addition, the device should be easy and inexpensive to use.